A National Security Agency computer technician with top secret security clearances was sentenced to 5.5 years in prison in U.S. District Court on Tuesday after he was convicted of removing “massive troves of highly classified national defense information without authorization” and keeping it at his home.

Nghia Hoang Pho, 68, of Ellicott City, Md., and a naturalized U.S. citizen born in Vietnam, was trained since 2006 in proper handling of classified information while working in the NSA’s Tailored Access Operations, the Justice Department said. He was authorized at the top secret and top secret/Sensitive Compartmented Information levels.

From 2010-2015, Pho removed and retained top secret U.S. government documents and writings that contained national defense information in both hard copy and digital form in several locations in his home, prosecutors said in a plea agreement. Pho knew he was not authorized to remove the material or store it at his home, and had signed several nondisclosure agreements, according to Justice.

“Pho’s intentional, reckless and illegal retention of highly classified information over the course of almost five years placed at risk our intelligence community’s capabilities and methods, rendering some of them unusable,” Assistant Attorney General for National Security John Demers said. “Today’s sentence reaffirms the expectations that the government places on those who have sworn to safeguard our nation’s secrets.”

U.S. Attorney for the District of Columbia and Maryland Robert Hur added, “As a result of his actions, Pho compromised some of our country’s most closely held types of intelligence, and forced NSA to abandon important initiatives to protect itself and its operational capabilities, at great economic and operational cost.”

The FBI special agent in charge in the Baltimore Field Office, Gordon Johnson, called the case “a clarion call to all security clearance holders to follow the law and policy regarding classified information storage. The FBI will leave no stone unturned to investigate those who compromise or mishandle classified information,” he said.